Each time a prospective creditor looks at your credit report, an inquiry notation is added to your file, and most inquiries stay on your credit report for up to two years. Inquiries you make yourself, inquiries made during screening for a pre-approved offer of credit, or an inquiry that is part of a background check for employment purposes are not reported to potential credit grantors.)

It is best to avoid over-applying for credit and running up excessive inquiries, for the simple reason that lenders of creditors may think you’re trying to get credit due to financial difficulty, or taking on more debt than you can repay.

Lenders do of course realize that some inquiries are a result of shopping around for the best rates on a loan, and so they will often overlook a block of inquiries within a very recent period. It may help if you explain the inquiries in the application process. 

Understanding how your credit report affects your financial future is the key to smart credit management. Incorporating a review of your credit report into your financial planning is also one of the best ways to make sure you meet your goals--especially when those goals involve major purchases, and you’re shopping for a loan with the most favorable terms possible.

source://http://www.credit-factor.com